Caption: Developing seeds of common Ash, Fraxinus excelsior. The picture shows an inflorescence with hundreds of seeds ( "ash keys") in August in the UK. The brown seeds are the most mature. Seed dispersal is by wind.Ash trees are wind-pollinated. Male and female flowers may occur in the same inflorescence, or in separate male-only or female-only inflorescences, or on male-only or female-only branches. This behaviour, and prolific seed production, means that ash trees show great genetic diversity. This is to the advantage of a population when faced with disease outbreaks, such as the current ash die-back, caused by Hymenoscyphus pseudoalbidus (formerly Chalara fraxinea) first noticed in the UK in 2012 at Ashwellthorpe Wood in Norfolk. The current outbreak will probably kill the majority of UK ash trees, but genetic diversity will ensure the long term survival of the population